A large feed lot uses two feed supplements, Ration I and Ration II. Each pound of Ration I contains 4 units of protein and 2 units of carbohydrates. Each pound of Ration II contains 3 units of protein and 6 units of carbohydrates. If the dietary requirement calls for 42 units of protein and 30 units of carbohydrates, how many pounds of each ration should be used to satisfy the requirements?